Instead of nagging eBay management for a PayPal spin-off, Carl Icahn should be asking it why it didn’t develop its own Airbnb. Yesterday, Airbnb raised its third round of venture capital, at a reported valuation of $10bn. The company functions as an eBay – for spare bedrooms in houses or flats, rather than household flotsam and jetsam. The brilliance of the business is that Airbnb doesn’t buy land and build hotels. It simply runs a website linking vacationers and residents. It doesn’t take much to build a website; it does take marketing acumen to build a sizeable user base before anyone else thinks of the idea.

Airbnb’s fees charge both the guest and the host and add up to between 9 per cent and 15 per cent of the base cost of the rental. At a $10bn valuation it is likely that the company, founded in 2008, has not yet hit $1bn in annual revenue (it has not yet disclosed results). Still, it boasts listings in 34,000 cities across 192 countries. Airbnb’s best marketing so far is word-of-mouth among satisfied customers. Its website profiles renters and customers so both sides of transactions can feel safe. High-end hotels catering to business travellers won’t sweat over Airbnb. But those who cater to budget travellers wanting just a room, or families on vacation, should be worried.

There are two factors that would-be Airbnb investors should monitor. The first is regulation. Out of concern for the public or (more likely) under the influence of hotel lobbyists, some local authorities have accused Airbnb of skirting existing lodging laws. Legal outcomes are hard to predict, whatever the benefits or risks to consumers. The second concern is valuation. Ebay’s marketplace unit has an estimated value of $35bn. But its 2013 revenue was nearly $7bn. An Airbnb rental is for the price-conscious. Its shares will not be.